The requirements for high areal density longitudinal recording impose increasingly greater requirements on thin film magnetic recording media in terms of coercivity, remanent squareness, low medium noise and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements, particularly a high density magnetic rigid disk medium for longitudinal recording.
The linear recording density can be increased by increasing the coercivity of the magnetic recording medium. However, this objective can only be accomplished by decreasing the medium noise, as by maintaining very fine magnetically noncoupled grains. Medium noise is a dominant factor restricting increased recording density of high density magnetic hard disk drives. Medium noise in thin films is attributed primarily to inhomogeneous grain size and intergranular exchange coupling. Therefore, in order to increase linear density, medium noise must be minimized by suitable microstructure control.
A substrate material conventionally employed in producing magnetic recording rigid disks comprises an aluminum-magnesium (Al-Mg) alloy. Such Al-Mg alloys are typically electrolessly plated with a layer of NiP at a thickness of about 15 microns to increase the hardness of the substrates, thereby providing a suitable surface for polishing to provide the requisite surface roughness or texture.
Other substrate materials have been employed, such as glasses, e.g., an amorphous glass, glass-ceramic materials which comprise a mixture of amorphous and crystalline materials, and ceramic materials. Glass-ceramic materials do not normally exhibit a crystalline surface. Glasses and glass-ceramics generally exhibit high resistance to shocks. The use of glass-based materials, such as glass-ceramic materials, is disclosed by Hoover et al., U.S. Pat. No. 5,273,834.
A conventional longitudinal recording disk medium is depicted in FIG. 1 and typically comprises a non-magnetic substrate 10 having sequentially deposited on each side thereof an underlayer 11, such as chromium (Cr) or a Cr-alloy, a magnetic layer 12, typically comprising a cobalt (Co) -base alloy, and a protective overcoat 13, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat (not shown) to the protective overcoat. Underlayer 11, magnetic layer 12 and protective overcoat 13 are typically deposited by sputtering techniques. The Co-base alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-alloy underlayer.
Conventional methods for manufacturing a magnetic recording medium with a glass or glass-ceramic substrate comprise applying a seed layer between the substrate and underlayer. Such magnetic recording media with glass or glass-ceramic substrates are commercially available from different manufacturers with different seed layer materials to reduce the effect of high thermal emissivity of such glass and glass-ceramic substrates, and to influence the crystallographic orientation of subsequently deposited underlayers and magnetic layers. Such conventional seed layer materials also include NiP which is typically sputter deposited on the surface of the glass or glass-ceramic substrate at a thickness of about 500 .ANG.. Sputtered NiP films on glass or glass-ceramic substrates were reported in the literature for the control of crystallographic orientation of the magnetic media and the enhancement of coercivity (for example, Hsiao-chu Tsai et al., "The Effects of Ni.sub.3 P- sublayer on the Properties of CoNiCr/Cr Media Using Different Substrates," IEEE Trans. on Magn., Vol. 28, p. 3093, 1992).
Conventional magnetic recording media comprising a glass or glass-ceramic substrate having NiP sputtered thereon also comprise, sequentially deposited thereon, a Cr or Cr-alloy underlayer at an appropriate thickness, e.g., about 550 .ANG., a magnetic layer such as Co-Cr-platinum (Pt)-tantalum (Ta) at an appropriate thickness, e.g., about 350 .ANG., and a protective carbon overcoat at an appropriate thickness, e.g., about 150 .ANG.. Conventional Cr-alloy underlayers comprise vanadium (V) or titanium (Ti). Other conventional magnetic layers are CoCrTa, CoCrPtB, CoCrPt and CoNiCr. The seed layer, underlayer, and magnetic layer are conventionally sequentially sputter deposited on the glass or glass-ceramic substrate in an inert gas atmosphere, such as an atmosphere of pure argon. A conventional protective carbon overcoat is typically deposited in a mixture of argon with nitrogen, hydrogen or ethylene. Conventional lubricant topcoats are typically about 20 .ANG. thick.
Magnetic films exhibiting a bicrystal cluster microstructure are expected to exhibit high coercivity, low noise and high remanent squareness. In co-pending application Ser. No. 08/586,571 filed on Jan. 16, 1996, now U.S. Pat. No. 5,830,584, issued Nov. 3, 1998, a magnetic recording medium is disclosed comprising a glass or glass-ceramic substrate and a magnetic layer exhibiting a bicrystal cluster microstructure. The formation of a bicrystal cluster microstructure is induced by oxidizing the surface of a seed layer so that the underlayer subsequently deposited thereon exhibits a (200) crystallographic orientation which, in turn, induces a bicrystal cluster microstructure in a magnetic alloy layer deposited and epitaxially grown on the underlayer.
U.S. Pat. No. 5,733,370 discloses a method of manufacturing a magnetic recording medium comprising a glass or glass-ceramic substrate and a magnetic layer exhibiting a bicrystal cluster microstructure. The disclosed method comprises sputter depositing an NiP seed layer on a glass or glass-ceramic substrate and subsequently oxidizing the deposited NiP seed layer. The oxidized upper seed layer surface induces the subsequently deposited underlayer to exhibit a (200) crystallographic orientation which, in turn, induces the magnetic alloy layer deposited and epitaxially grown on the underlayer to exhibit a bicrystal cluster microstructure. The magnetic recording media disclosed in co-pending application Ser. No. 08/586,571, now U.S. Pat. No. 5,830,584 and U.S. Pat. No. 5,733,370 exhibit high coercivity, low magnetic remanence (Mr) x thickness (t) and low noise, thereby rendering them particularly suitable for longitudinal recording. The entire disclosures of U.S. Pat. No. 5,830,584 and U.S. Pat. No. 5,733,370 are incorporated by reference herein.
After extensive experimentation and investigation, it was found that the adhesion between seed layers, particularly nickel-phosphorous seed layers, and non-conventional substrates, such as glass, ceramic or glass-ceramic substrates, is undesirably low and is not suitable for certain applications, as in high temperature and high humidity environments. Accordingly, there exists a need to enhance the adhesion between seed layers, such as nickel-phosphorous layers, and alternate substrates, such as glass, ceramic, or glass-ceramic substrates, to produce a magnetic rigid disk media for longitudinal recording, in various types of environments, exhibiting low medium noise and high coercivity in an efficient, cost-effective manner with high production throughput.